Best available copy



D. G. McCAA.

CONTROLLING APPARATUS FOR WIRELESS TELEPHONE SYSTEMS.

APPLICATION FILED mm: 4.19m

1,304,188. Patented May 20, 1919.

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DAVID G. MoCAA, 0F LANCASTER, PENNSYLVANIA.

CONTROLLING APPARATUS FOR WIRELESS TELEPHONE SYSTEMS.

Application filed June 4, 1918.

To all whom it may concern:

Be it known that I, DAVID G. MCGAA, a citizen of the United States,residing in Lancaster, Pennsylvania, have invented the Con trollingApparatus for Wireless Telephone Systems, of which the following is aspecification.

As is known to those skilled in the art of radio telephony, if a sourceof persistent electrical oscillations of high frequency be electricallycoupled to a radiating circuit, the placing of a microphone either inthe generating or in the radiating circuit renders it possible tomodulate the energy continuously radiated by and in accordance withsound. Generators of persistent oscillations such as the oscillatoryarc, when employed in radio telephony, cause more or less objectionablehissing sounds, in addition to those caused by the sound-actuatedtransmitting mechanlsm, to be heard at the receiving station, du to thesuperposition of the variations in the radiated current resulting fromsuch gene-rators, upon the variations caused by the sound actuatedmechanism. The sounds re ferred to are constantly heard between thesound signals or words and in some cases are of such intensity as tointerfere with the clear reception of the transmitted sound. One objectof my invention therefore, is to provide a system or combination ofappara: tus of the general character indicated, which shall be sodesigned and assembled that there shall be none of the above notedobjectionable noises in the receiving instrument and in which only soundmodulated energy will be radiated.

It is further desired to provide a system of the above typewhich shallinclude a novel arrangement of apparatus whereby a given antenna currentis modified by and in accordance with current variations in a microphonecircuit, so related to or associated with the antenna circuit that thecurrent in the former may be materially less than has hitherto beenconsidered permissible in order to attain the desired results.

These objects and other advantageous ends I attain as hereinafter setforth, reference being had to the accompanying drawings, in Iwhich-Figure 1 is a diagrammatic illustration of the preferred arrangement ofapparatus constituting my invention; and

Figs. 2 and 3 are fragmentary diagrams illustrating modifications of myinvention.

Specification of Letters Patent.

Patented May 20, 1919.

Serial No. 238,176.

In the above drawings, 1 represents a high frequency alternating currentgenerator in whose circuit is connected a primary transformer winding 2which with it is so designed as to constitute a primary source ofpersistent high frequency oscillations. Inductively associated with thisprimary Winding is a secondary winding 3 forming part of an openradiating circuit consisting of an antenna in the form of elevatedconductors 4, a variable inductance 5, and the earth plate or groundconnection 6. In addition to the secondary windin 3, there is aconnection between the in uctance 5 and the ground connection 6including a second adjustable inductance 7.

This latter inductance serves as the primary winding of a transformerhaving two secondary windings 8 and 9 of the same number of turns andeach adjustable as to the number of turns in circuit. The first of thesesecondary windings 8 is connected in a closed circuit including a bod 10of noninductive resistance and an in uctance 13, while the secondwinding is similarly connected in a closed circuit including amicrophone 11 and an inductance 12. The two coils 12 and 13 areinductively associated and are adjustable so that they both have thesame number of turns under any given operating conditions.

Disregarding for the time being the elements 7-11 with their associatedcircuit connections, it will be noted that by adjustments of theinductance values of the elements 2, 3 and 5, the open radiating systemmay be caused to absorb energy from the primary source 12 and to radiateit into space. At any given wave length, this function is a maximum whena hot wire or thermocouple meter gives the highest reading.

If when the system is adjusted for maximum radiation at a given orselected wave length, the inductance coil 7 be connected across or inshunt to that portion of the antenna system which is receiving energyfrom the primary source of supply, 15, 0., the secondary winding 3,there will be but littie change in the current flow provided thereactance value of the inserted inductance is sufliciently high to causethe antenna oscillations tofollowthe path 4 -5-3 6 rather than the path457'6. Any slight change in the radiated wave may be compensated for byvarying the value of the inductance 5, although if the reactance of thecoil 7 is too small, the radiated wave will be of a reduced length andthe coupling of the antenna system with the primary winding will not beso close as heretofore.

Obviously if a secondary circuit should be closely coupled to theinductance 7 and if said circuit should be closed, the reactance valueof said coil 7 will fall as a result of the counter-action of itsmagnetic field by the secondary current. WVith the reactive value of thecoil 7 thus practically eliminated, the shunt path in which it isincluded presents but a low ohmic resistance and consequently acts as ashort circuit across the secondary coil 3, cutting off the radiatingcircuit from the source of supply and causing the antenna current tofall to practically zero. Even if a feeble antenna current should flowthrough the circuit 457-6, the slight radiation resulting would be at amaterially reduced wave length.

A variation of the current in the closed secondary system associatedwith the inductance 7 causes the antenna current to divide between thecircuits 4-53-6 and 4576, so that the energy from the primary source 12is admitted to or cut off from the antenna to a varying degree dependingupon the rise and fall of the current in the secondary circuit whichvaries the reactance value of the coil 7. The introduction of resistanceinto the secondary circuit associated withthe coil 7 reduces thesecondary current, permits the reactance of the coil 7 to increase andcauses said coil to fail to short circuit the secondary coil 3,admitting energy from the primary source of supply into the radiatingsystem and altering the effective inductance of the antenna circuit. Asa result the antenna system is brought to a natural period correspondingwith the maximum radiation and the antenna current will thereforeincrease in value. Vice versa, decreasing the resistance of thesecondary circuit associated with the coil 7 will operate to reduce theantenna current by a reversal of the op erations outlined above.

If a microphone be connected in the secondary circuit associated withthe coil 7, as has been described and claimed in an application forUnited States Patent filed by me under date of June 13, 1916, Serial No.103,452, I have found that only a voice modulated current is admitted tothe antenna.

If as shown in Fig. 1, there are associated with the inductance orprimary coil 7 the two secondary coils 8 and 9, closely coupled to itand having the same number of turns, then said coils if connected inclosed circuits, will have equal currents induced in them regardless ofWhether the number of secondary turns in each coil is lessor more thanthat of the coil 7. Obviously if the circuits of these coils 8 and 9 areotherwise independent, the opening of one of them will allow the otherto absorb all of the energy from the primary coil. If however, as shownin Fig. 1, said circuits are iuductively and closely coupled by means ofthe two inductance coils 12 and 13, there is the same division ofprimary energy between them provided there is a reciprocal counteractionof said coils by reason of the current flow through them and this willdepend upon the circuit arrangement or manner of connecting them to thesecondary circuits.

If one secondary circuit, for example that of the coil 8, be opened, thecurrent in the other will at once dro practically to zero for the reasonthat the lnductance 13 fails to counteract the reactance of the coil 12,which is of such design as to completely block or choke off the currentnormally flowing in the circuit of the coil 9 when the circuit of thecoil 8 is closed. The same action will result if the circuit of the coil9 be opened, for then the coil 12 fails to neutralize the reactance ofthe coil 13 and this, as in the first case, chokes off the current flowin the coil 8.

Any decrease of the current in the circuit 81013 will cause thereactance value of the coil 12 to increase because of the failure of theinductance 13 to completely counteract it, and there will consequentlybe a decrease of the current in the secondary circuit 91112, the actionbeing reciprocal betwcn the two circuits. There is therefore, a serieseffect in the paralleled secondary circuits, since decrease of currentin one, instead of causing an increase in the other as is usual inparalleled circuits, will cause a decrease in current and vice versa.The microphone 11 in the circuit 91112 will thus cause variations in thereactance Value of the coil 7 under operating conditions, although it isnoticeable that this result is attained by the direct modulation of buta pa it of the total energy supplied from said 001 By repeatedexperiments I have found that the antenna current will not rise norincrease in value until more than a certain resistance is inserted inone of the secondary circuits, for example 81013, and since the currentnormal to these circuits is reduced by this inserted resistance, but afractional part of such current is required to maintain the antennacurrent practically zero. As a result of this arrangement which involvesthe non-inductive resistance 10, the microphone is called on to modulatecurrent values materially less than have hitherto been foundpracticable. That is to say, modulation of the reduced current in thecircuit 9'1112 will cause complete modulation of all the energyavailable in the antenna circuit, the antenna current rising and fallingwith the increase and decrease of resistance in the microphone. As anexample I have found thatantenna currents of ten amperes have beenmodulated fully when a current of one and onchalf amperes was presentand modulated in the microphone circuit.

It will be understood that without depart ing from my invention, theresistance 10 of the system shown in Fig. 1, instead of being insertedin but one of the secondary circuits, may be divided and one part 14 beconnected in the circuit 813 while the other part 15 is connected in thesecondary circuit 9-12. Similarly, instead of a single microphone in oneof the secondary circuits, there may be two microphones 11 and 11connected respectively in the circuits of the two secondary coils 8 and9. It is to be noted that the transformation ratio between the coil 7and the coils 8 and 9 may be either step-up or step doivn, although Iprefer the step-down ratio as this permits lower voltages in themicrophone.

If it be desired to still further reduce the current flow in themicrophone circuit, I may substitute for the microphone in the circuit91211 an inductance 16 of such value as to be capable of completelyblocking the flow of current in said circuit. It is then possible toassociate with this inductance two other inductive windings 17 and 18,of which the first is included in a circuit having also connected in ita fixed non'inductive resistance 19 and an inductance 20 operativelyassociated with an inductance 21 included in circuit with the coil 18and a microphone 22. The action of the system comprised by the circuits1.720 19 and 182122, upon the coil 16 and the circuit of which it formsa part, is similar to that previously described in connection with thearrangement illustrated in Fig. 1, and as above indicated, therelatively small current flow in the circuit 182122, which is modulatedor varied by and in accordance with the sound waves acting on themicrophone, acts upon and causes corresponding variations of the muchgreater current of the antenna circuitsand that without causing orinvolving the objectionable hissing sounds in the receiving apparatuswhich would otherwise be present.

By these means there is admitted to the antenna only sound modulatedcurrent whose envelop curve presents steep variations in amplitude whichextinguish by the sound produced in a receiver, the slight variationsdue to irregularities in the generator.

I claim:

1. The combination in a transmitting system of a branched radiatingcircuit; a source of high frequency oscillations operatively connectedto one branch of said circuit; a primary transformer winding connectedin the other branch of the radiating circuit; a plurality of auxiliarycircuits each including a secondary winding inductively associated withsaid primary winding; means operatively associated with one of saidauxiliary circuits for varyin the current flow therein by and in accorance with sound; and means independent of said secondary windings forinductively connecting said auxiliary circuits.

2. The combination in a transmitting system of a radiating circuit; asource of high frequency oscillations operatively connected to saidcircuit; two inductively coacting auxiliary circuits also connected tosaid circuit; with means operatively connected to one of said auxiliarycircuits for modulating the current flow therein by and in accordancewith sound.

3. The combination in a transmitting system of a radiating circuit; asource of high frequency oscillations operatively connected to saidcircuit; two inductively coacting auxiliary circuits inductivelyconnected to said first circuit; and a mlcrophone connected in one ofsaid auxiliary circuits.

4. The combination in a transmitting system of a radiating circuit; asource of high frequency oscillations operatively connected to saidcircuit; a primary transformer winding also connected in said circuit; aplurality of auxiliary circuits respectively including secondarywindings coasting with said primary winding; means connected in one ofthe auxiliary circuits for causing the current flow therein to be variedby and in accordance with sound and means for causing the currents inthe auxiliary circuits to rise and fall simultaneously.

5. The combination in a transmitting system of a branched radiatingcircuit; a source of high frequency oscillations operatively connectedto one branch of said circuit; a primary transformer winding in theother branch of said circuit; a plurality of auxiliary circuitsrespectively including secondary windings coacting with said primarywinding; means connected in one of the auxiliary circuits for causingthe current flow therein to be varied by and in accord ance with sound;and means consisting of coacting inductances respectively connected insaid circuits for causing the currents therein to rise and fallsimultaneously.

6. The combination in a transmitting system of a radiating circuit; asource of high frequency oscillations operatively connected to saidcircuit; a primary transformer winding also connected in said circuit; aplurality of auxiliary circuits respectively including secondarywindings coacting with said primary winding and designed in stepdownratio thereto; means for modulating the current flow in one of theauxiliary circuits by and in accordance with sound; and meansindependent of the secondary windings for causing said auxiliarycircuits to mutually react one upon the other.

7. The combination in a transmitting system of a radiating circuit; asource of high frequency oscillations operatively connected to saidcircuit; a primary transformer winding also connected in said circuit; aplurality of auxiliary circuits respectively in cluding secondarywindings coacting with said primary winding; a resistance in one of theauxiliary circuits; means connected in the other circuit for modulatingthe current flow therein by and in accordance with sound; and coactiveinductances respectively connected in the auxiliary circuits.

8. The combination in a transmitting system of a radiating circuit; asource of high frequency oscillations and a primary transformer windingoperatively connected to said circuit; a plurality of auxiliary cirouitsinductively associated with said primary winding; means for causingcurrent flow in the auxiliary circuits to simultaneously and equallyrise and fall; and means for causing the current flow in the auxiliarycircuits to be varied by and in accordance with sound.

9. The combination in a transmitting system of a radiating circuitincluding a primary transformer winding; a plurality of auxiliarycircuits respectively including secondary windings inductivelyassociated with said primary winding; means inde pendent of saidwindings for causing current flow in one of the auxiliary circuits tovary directly as the current flow in the other auxiliary circuit isvaried; and means for modulating the current How in one of the auxiliarycircuits by and in accordance with sound.

In witness whereof I afiix my signature.

DAVID G. MCCAA.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. 0.

